Our results indicated that M2 stage in HCC may be associated with lower complement C3 levels, tumor size > 5 cm, incomplete tumor capsules, and late Edmondson–Steiner grade. Using these influencing factors, we developed a nomogram model that could effectively distinguish the presence of M2 in patients with HCC.
The long-term prognosis of patients with HCC remains poor in the early to middle stages after treatment, which is mainly due to the high recurrence rate after primary resection caused by de novo tumors resulting from intrahepatic metastasis or underlying liver pathologies.[6, 28] MVI, considered an important marker of aggressive behavior in HCC, can significantly affect the intrahepatic metastasis of tumor cells through the portal circulation, leading to tumor recurrence after curative surgery. [29]For MVI to occur, the cancer cells must acquire the ability to disrupt ligation/adhesion, decompose the extracellular matrix, and migrate to and utilize alternative energy sources. These changes are commonly observed during epithelial-to-mesenchymal transition (EMT), in which malignant cells de-differentiate from a polar, adherent phenotype to a mobile mesenchymal state with a more aggressive and resilient biology.[30] Increasing evidence suggests that the presence of MVI is associated with detection of the EMT phenotype in primary tumors. In MVI-positive cases, M2 grade is an obvious indicator of poor prognosis in HCC.[31] Myeloid cells and macrophages in the tumor microenvironment of HCC promote MVI and tumor progression through midkine proteins, providing favorable conditions for rapid tumor growth and invasion. [32]Unfortunately, M2 classification can only be diagnosed by histopathological examination after surgical resection; therefore, we need to look for important risk factors for MVI and its M2 grade and develop predictive models to make optimal clinical decisions, which may have important implications for postoperative recurrence detection and anti-recurrence strategies in patients with HCC.
In this study, approximately 19.51% of patients with HCC (88/451) were classified as M2 grade. Our results suggesting significant differences in OS and RFS between
M0-1 and M2 patients, with a shorter RFS and OS observed in M2 patients. These results are comparable with Yao et al. [9] who reported similar findings, which may be related to the similar baseline settings in both studies. We used LASSO, Boruta, XGboost, and Best_subset to screen the four machine learning methods by five-fold cross-validation and used the intersection to derive the most important factors related to M2.
Complement C3 is a plasma protein synthesized by the liver and macrophages and is a key component of the complement system. C3 has the highest complement content and plays a central role. The complement system is an important component of the immune system and can be activated through multiple pathways. C3b binds to the surface of the pathogen and facilitates its clearance through multiple pathways. In addition, complement C3 participates in processes such as cytotoxicity, the inflammatory response, and the removal of pathogenic microorganisms to enhance the body's ability to resist infection. Moreover, complement C3 increases vascular permeability, virus neutralization, and cytolysis. C3 is an important component of the immune system and plays an important role in maintaining immune balance and resisting infection. Studies have shown that serum fatty acids, adipose tissue-derived cytokines, and gut-derived endotoxins participate in complement activation. Following complement activation, C3 interacts with different types of hepatic innate immune cells, ultimately participating in the pathogenesis of non-alcoholic fatty liver disease (NAFLD).[33] Other studies have shown that the liver synthesizes most blood proteins, except γ -globin, liver damage reduces the synthesis of C3 and C4, and that hepatitis B virus (HBV) infection may induce the formation of various antigen–antibody complexes, which activate the complement system, leading to excessive consumption of complement components including C3 and C4. It is well known that HBV infection, as well as NAFLD, are important factors in the development of HCC.[34] Other studies have shown that PIWIL1 induces HCC cells to secrete complement C3, which mediates HCC through the interaction of cells and myeloid-derived suppressor cells (MDSCs), initiating the expression of the immunosuppressive cytokine IL-10. Neutralizing IL-10 secretion reduces the immunosuppressive activity of MDSCs in the HCC microenvironment with PIWIL1 expression, thereby promoting the initiation, development, and progression of HCC.[35] However, few studies have investigated the association between complement C3 and MVI. In our study, the OR for complement C3 was < 1, indicating that complement C3 is a protective factor.
Studies have shown that tumor aggressiveness increases with an increase in tumor size, and that tumor size is correlated with MVI.[36] A study from an international multicentre database showed that the incidence of MVI increased with the size of the resected HCC tumors. [37]Histological examination revealed that venous invasion-positive tumors had a strong tendency for invasion, resulting in an irregular tumor margin irregular and incomplete capsule. A radiomics-based study demonstrated that tumor size and incomplete capsules were highly reliable predictors of MVI.[38, 39] In a prediction model, Chen et al.[40] showed that an incomplete tumor capsule is an important factor for predicting M2. Similarly, in our study, an incomplete tumor capsule was shown to be an independent risk factor for M2.
The Edmondson-Steiner grade is used to evaluate the malignancy of HCC based on the morphological and histological characteristics of tumor cells, and grades I and II represent high levels of differentiation, while grades III and IV represent poorly differentiated and undifferentiated tumors, respectively. The Edmondson-Steiner grade has been shown to be associated with the prognosis of HCC.[41]MVI and Edmondson-Steiner grades are important components of the pathological grade of HCC. Several predictive models have linked the Edmondson–Steiner classification to MVI.[42] Our study found that clinical Edmondson–Steiner type was significantly associated with M2 and was an independent predictor of M2 grade, implying that a Edmondson–Steiner classification indicating poor cellular differentiation corresponds to a worse MVI grade.
In a recent randomized controlled study of BCLC-A stage, a tumor diameter of 5 cm was associated with high-risk MVI. The disease-free survival rates at 1, 2, 3, and 5 years were 86.7%, 76.7%, 60.0%, and 56.3%, respectively. In contrast, in the intention-to-treat population, the survival rates in the surgery-alone group were 90.0%, 66.7%, 52.8%, and 45.7%, respectively (P = 0.448). No statistically significant difference in the survival outcome was observed between neoadjuvant radiotherapy and upfront surgery in patients with early HCC and those with a high MVI risk.[43] Studies have also shown that postoperative adjuvant transcatheter arterial chemoembolization(TACE) is beneficial for patients with middle- and advanced-stage HCC and MVI.[44] Ueshima K et al. [45] showed that hepatic arterial infusion chemotherapy(HAIC) is a potential first-line treatment option for patients with advanced HCC and MVI but without distant metastasis. In a recent study, Wang K et al. [46]showed significantly prolonged RFS with MVI (median RFS: 27.7 months vs 15.5 months; HR: 0.534, 95% CI: 0.360–0.792; P = 0.002). Many studies have shown that for MVI and high-risk, resectable HCC patients, active preoperative neoadjuvant therapy other than radiotherapy may improve RFS and OS; therefore, more aggressive treatment options should be adopted for patients with M2 grade HCC.[31]
The nomogram is considered a user-friendly and practical prediction tool with high accuracy and good discriminative power and is widely used for the evaluation of prognostic or prognostic events.[47] Therefore, we developed a nomogram combining C3 level, tumor size, tumor envelope integrity, and Edmondson–Steiner grade to predict M2. According to the optimal calibration curve, the predicted probabilities were in good agreement with the actual observed values. In training set, the AUC was 0.765 (95% CI: 0.696–0.843), and in validation set, it was 0.807 (95% CI: 0.712–0.903). The optimal cut-off probability obtained using the ROC curve was 0.185, and the M2 total score was calculated according to the nomogram. The DCA results showed that the use of a nomogram to predict M2 may add more benefit than treating all patients, with or without any patients in the training and validation sets. The CIC results indicated that the predictive power of the nomogram model was significant.
It is important to note that this study had several limitations. First, all patients with HCC in our study tested positive for HBsAg. Although the established nomogram showed satisfactory discriminatory performance, our prediction model may only be applicable to HCC caused by HBV and does not consider HCC caused by hepatitis C virus or non-alcoholic/alcoholic hepatitis.[48] Second, this study had a small sample size, was retrospective, and inevitably had case–selection bias. Therefore, a prospective study with a balanced population and a large sample size is required to confirm the reliability of our nomogram. Third, our study was conducted in one study unit without any validation; it is necessary to validate our results using data from multiple centres. Finally, because the model was based on clinicopathological data, the mechanisms leading to early relapse and metastasis in M2 patients remain unclear, and the accuracy may be further improved if specific markers of M2 are added.
In conclusion, complement C3, tumor size > 5 cm, incomplete tumor capsule, and Edmondson–Steiner stages III–IV were identified as important predictors for the development of M2 in patients with HCC. We then combined the above variables to create a practical nomogram to make the individualized prediction of the M2 rank more objective and accurate. According to the nomogram scoring system, if patients are considered to be at a high risk of M2, more aggressive and precise treatment is tailored to reduce the potential risk of recurrence. Finally, our nomogram could improve individualized treatment designs and facilitate the selection of surveillance plans to develop more effective treatment options for patients with HCC.